bignum_mod_raw.py: Added BignumModRawOperation
bignum_mod_raw.py: Added BignumModRawOperation

This patch is adding a basic instantance of `BignumModRawOperation`
and creates an `BignumModRawOperationArchSplit` class, copying
over the implementation of `BignumCoreRawOperationArchSplit`.

Signed-off-by: Minos Galanakis <bb9c15d46ed7ecad5455c4c22ac024636068eda6@arm.com>

ARMmbed/mbedtls,ARMmbed/mbedtls,Mbed-TLS/mbedtls,ARMmbed/mbedtls,Mbed-TLS/mbedtls,Mbed-TLS/mbedtls,ARMmbed/mbedtls,Mbed-TLS/mbedtls